Metallica’s Robert Trujillo and Kirk Hammett were back at it last night (Apr. 11), paying homage to the late bassist Martin Eric Ain of local metal heroes Celtic Frost at the band's WorldWired Tour stop in Geneva, Switzerland. During the nightly "doodle" segment featuring the two, they performed "Procreation (of the Wicked)," with Trujillo on vocals.

"Tonight, we pay tribute to the Swiss band, Celtic Frost," Trujillo says while introducing the song in a clip which can be viewed above. "This is in memory of Mr. Martin Eric Ain, bass player extraordinaire, and this song is called "Procreation"...you know the rest. Sing it with me or headbang like it's 1984!"

"Procreation (of the Wicked)" opened the second side of Celtic Frost's 1984 influential debut LP Morbid Tales. The record is credited with playing a major part in shaping the development of European thrash, death and black metal. Ain, who was born Martin Stricker, died of a heart attack this past October.

Trujillo and Hammett have been making the most of their time together each night after the rest of the band takes a break following the playing of the song "Halo on Fire," taking the the opportunity to recognize an artist from the European cities in which they are performing.

Next up for Metallica is a return to the States for the sixth annual "Metallica Night" with the San Francisco Giants on Monday, April 23. They then head back to Europe until early May before taking off for the summer and returning to the road in North America for a run of arena dates. The full list of upcoming shows can be found here.